Douglas Isbell
Headquarters, Washington, DC June 25, 1999
(Phone: 202/358-1547)
Lynn Jenner
Goddard Space Flight Center, Greenbelt, MD
(Phone: 301/286-8982)
RELEASE: 99-74
INVESTIGATION FINDS DESIGN ERRORS
CAUSED WIRE SPACECRAFT FAILURE
NASA's Wide-Field Infrared Explorer (WIRE) failed because of an
incorrectly designed electronics box that prematurely fired explosive
devices, causing early ejection of the instrument's telescope cover, a
NASA board has found.
The WIRE Mishap Investigation Board found that the design of the
instrument's electronics box did not take into account subtle, but
known, start-up characteristics of one component within the box.
Electrical power created at the start-up of this component reached
explosive devices, called pyrotechnics, meant to eject the telescope's
cover later in the mission. The power reached the pyrotechnics within a
fraction of a second after the box was turned on, and the cover was
ejected.
With the premature loss of the telescope's cover, the frozen
hydrogen used to cool the telescope's sensitive infrared detectors was
exposed to the Sun. As the telescope warmed, the hydrogen converted into
a gas and vented entirely into space within 48 hours of launch. Without
the frozen hydrogen, the instrument could not conduct its scientific
mission.
"There was no component failure," said Darrell Branscome, chairman
of the eight-member WIRE Mishap Board and Deputy Associate Administrator
(Enterprise Development) for NASA's Office of Space Flight, Washington,
DC. "This was simply a case of a design error that allowed power to get
to the explosive charges before it should have. The system operated the
way it was designed. Unfortunately, the design was flawed."
The report added that simulators and other support equipment used
for design and verification tests lacked the fidelity required to detect
this potential failure.
"A significant contributing cause of the anomaly was the failure to
identify, understand, and correct the electronic design of the pyro
electronics box," the report said. "Design errors in the circuitry,
which controlled pyro functions, were not identified. The pyro
electronics box design was not peer reviewed, and other system reviews
conducted by the instrument design team did not focus on the electronics
box."
WIRE was launched from Vandenberg Air Force Base, CA, March 4
aboard a Pegasus XL launch vehicle. WIRE's mission was to detect
infrared light in the background cosmos to learn more about the
formation of stars, galaxies and the current state of the universe.
NASA has already taken additional steps to ensure that design
engineers are aware of this condition. A NASA Parts Advisory was issued
on May 27 at the request of the Mishap Board informing design engineers
of the need to consider the startup behavior of electronic devices to
prevent unwanted or unexpected power discharges.
The team's report also included recommendations for future
spacecraft designers. These include the use of independent, separate
inhibiting devices for pyrotechnics for mission-critical or irreversible
events; additional testing for anomalous start-up behavior; detailed,
independent reviews to assess the system design; and consideration of
the design, location and mounting of external vent hardware in the event
of a worst-case venting scenario.
The WIRE spacecraft is now in a stable orbit with its other systems
and electronics in good working order. Ground controllers will proceed
with tests on new flight-control technology aboard the spacecraft.
The WIRE mission was the latest in a series of Small Explorers, a
project under the Explorers Program managed by NASA's Goddard Space
Flight Center, Greenbelt, MD. Goddard also built the WIRE spacecraft.
The Jet Propulsion Laboratory, Pasadena, CA, managed development of the
WIRE instrument, which was constructed by the Space Dynamics Laboratory
at Utah State University, North Logan, Utah.
The full text of the executive summary of the report is available
on the World Wide Web
at:
ftp://ftp.hq.nasa.gov/pub/pao/reports/1999/wire_summary.pdf
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